Noise-driven Plasma Instabilities Relevant to Generations of the Flow and the Field

Abstract

The stability of a magnetohydrodynamic (MHD) plsma that is forced by external noise is explored. The noise is assumed to be of a Gaussian nature and to have both isotropic and anistropic components with a preferential direction (s) over cap. If the anisotropic part of the noise auto-correlation spectrum is not invariant under reflection (i.e., parity non-conserving, PNC), an antisymmetric component with respect to (s) over cap, the so-called dynamo a term is found to be induced in the evolution of the magentic field and may cause a magnetic perturbtion to grow. In contrast, if the PNC noise spectrum is symmetric, the noise induces a kinetic response that destabilizes the plasma. If the magnitudes of the kinetic and the magnetic noises are of the same order, the kinetic noise contributes dominantly to the instability when the magnetic Prandtl number is small. We argue that the macroscopic field and flow are more prone to instability and may exist in the steady state where nonlinear effects saturate the noise-induced growth.